Turbines



Oct. 31, 1961 Filed March 9, 1959 A. THOMAS TURBINES 2 Sheets-Sheet 1 Oct. 31, 1961 TURBINES Filed March 9, 1959 A. THOMAS 2 Sheets-Sheet 2 a mm Inventor ALBERT THaNAS Attorneys United States Patent P 3,006,355 TURBINES Albert Thomas, Coventry, England, assignor, by mesne assignments, to Bristol SiddeIey Engines Limited,

Bristol, England, a British company Filed Mar. 9, 1959, Ser. No. 798,202 Claims priority, application Great Britain Mar. 13, 1958 4 Claims. (Cl. 137-31) The invention relates to turbines and is particularly concerned with the provision of an overspeed trip for a free power turbine.

If the free turbine is suddenly isolated from its load through any cause, the speed will increase rapidly in a very short time. In such an eventuality although a safe overspeed of the turbine may be permitted, on no account must the turbine be allowed to run at a higher speed than the permitted overspeed as in a matter of seconds the turbine could run away and distintegrate. An object of the invention is to provide an overspeed trip which will act substantially instantaneously to shut down the turbine.

According to the invention a turbine overspeed trip comprises centrifugally-operable trigger means rotatable with the turbine, the trigger means being operable at a predetermined speed to interrupt the supply of fuel to combustion chamber means arranged to supply working gases to the turbine.

The trigger means may comprise a plurality of symmetrically arranged radially-extending arms rotatable with the turbine and each held at a position spaced radially from the axis of rotation of the turbine, each arm having an extension in the axial direction nearer to the axis of rotation than the holding position and being biased against centrifugal force, the biasing being sutficient only to resist centrifugal force until the said predetermined speed has been reached, the arms being deflected outwardly about their holding positions at said predetermined speed to interrupt the said supply of fuel. Preferably, the biasing is effected by so pre-stressing the arms that they tend to spring in a direction opposed to the direction of the centrifugal deflection, abutment means being provided to limit movement of the arms in the said opposed direction.

By way of example, an overspeed trip for a free power turbine of a gas turbine engine will now be described with reference to the accompanying drawings, in which:

FIGURE 1 shows diagrammatically the lay-out of the engine;

FIGURE 2 is an axial section through the engine in the vicinity of the power turbine and shows the overspeed trip in its normal position; and

FIGURE 3 shows part of FIGURE 2, drawn to a larger scale, the overspeed trip being in the tripped position.

Referring firstly to FIGURE 1, the engine comprises a compressor 1, mechanically coupled to a gas turbine 2, which supplies exhaust gases to a free power turbine 3. The shaft 9 of the turbine 3 carries an overspeed trip 4. A combustion chamber 5, arranged to receive air from the compressor 1 and to supply hot gases to the gas turbine 2 is connected by pipes 6 and 7 to a source of fuel. The pipes 6 and 7 communicate with a shut-off valve 8, under the control of the overspeed trip 4. The overspeed trip 4 and the valve 8 will now be described more fully with reference to FIGURES 2 and 3.

In FIGURE 2, the free power turbine 3 mounted on the shaft 9 is shown in axial section. The overspeed trip 4 comprises a disc 10 attached to the shaft 9 for coaxial rotation therewith. The disc 10 carries two L-shaped arms 11 which are supported symmetrically on the disc and are each arranged with one limb of the. L-shaped arm adjacent a face of the disc 10 and extending in a substantially radial direction and with the other limb ex 3,006,355 Patented Oct. 31, 1961 tending in a substantially axial direction. The limb adjacent the disc face is rigidly attached at 12 at the radiallyouter end near the periphery of the disc and the arm is so shaped that when it is mounted in position. adjacent the face of the disc it is pre-stressed, so that it tends to spring in a direction opposed to that of deflection due to centrifugal force. The arms 11 are held in their pro-stressed condition by mutual engagement of the radially-inner surfaces of the axially-extending limbs thereof, as shown in FIGURE 2. The free end of the axially-extendinglimb of each L-shaped arm carries a cutting blade 13, which is deflected to the position shown in FIGURE 3, when. a predetermined speed has been reached at which the centrifugal force acting on the arm has overcome the prestressing. In the deflected position, the radially-extending limb of each armv will assume a position adjacent a casing 14, secured at its periphery to the disc 10, by bolts 12, which also hold the L-shaped arms 11. The axiallyextending limbs of the arms 11 carry pins 15, which are internally screwed to the limbs for fine adjustment in the axial direction, so that simultaneous deflection of both arms at the predetermined speed can be ensured.

The valve 8 comprises a valve member 18' which is urged by a helical compression spring 19 towards its seat 20. A rod 21 connected to the valve member 18 extends towards the axis of the engine and is held radially inwards, against the bias of the spring 19, by a heat-resistant metal tape 22, which is anchored, at 23 at the end remote from the rod 21, to a member 24 rigidly fixed to a stationary part of the engine. A radially-inner face of the member 24 contains a slot 25 across which the tape is held in tension by the spring 19, as shown in FIGURE 2. In this position the tape 22 holds the valve member away from its seat. When the arms 11 deflect under centrifugal force to the positions shown in FIGURE 3 the first blade 13 to engage the tape will cut the tape in the vicinity of the slot 25 and the spring 19 will immediately be released and will close the valve, thereby causing interruption of the fuel supply to the combustion chamber and the shutting down of the turbines 2 and 3.

Instead of a disc attached to the turbine, a spider in the form of a number of radially-extending spokes may be provided. The arms would be attached to the outer ends of the spokes and could be held in a pre-stressed condition in similar manner to that shown in FIGURE 2.

Instead of employing a cutter and tape, the arms 11 can, on deflection due to centrifugal force, actuate any other suitable mechanism for releasing the rod 21.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A gas turbine engine including a turbine, combustion chamber means capable of supplying working gases to said turbine, means for supplying fuel to said combustion chamber means, means for interrupting said supply of fuel and centrifugally-operable trigger means comprising a plurality of symmetrically-arranged radially-extending arms rotatable with the turbine and each held at a position spaced radially from the axis of rotation of the turbine, each arm having an extension in the axial direction at the radially-inner end thereof and being biased against centrifugal force by so pre-stressing the arms that they tend to spring in a direction opposed to the direction of the centrifugal deflection, abutment means being provided to limit movement of the arms in the said opposed direction, the biasing being suflicient only to resist centrifugal force until a predetermined speed has been reached, the arms being deflected outwardly about their holding positions at said predetermined speed to actuate said interrupting means.

2. A gas turbine engine as claimed in claim 1 in which the arms are attached at their radially outer ends to a disc rotatable with the turbine, the radially inner surfaces of the axial extensions of the arms being arranged to engage one another to provide the abutment means to hold the arms in a pre-stres sed condition. 7 i v I 3. A gas turbine engine supplying pressurized fluid to a free power turbine having an overspeed trip comprising a disc rotatable with the free power turbine, a pair of radially-extending arms each attached to the periphery of the disc at diametrically opposite positions and each having an axially-extending limb at the radially-inner end thereof, the arms being so pre-stressed that they are biased towards the adjacent face of the disc in opposition to centrifugal V 7 force tending to deflect the arms outwardly away from the face of the disc, the biasing being sufficient only to resist centrifugal force until a predetermined speed has been reached, a cutting blade carried on each axially-extending limb and a stop valve in a fuel supply pipe to a combustion chamber of the engine, the stop valve being normally held open against the action of a compression spring by a tape, anchored at one end to a fixed part of the engine and attached at the other end to a closure member of the stop valve, the tape being positioned in the path followed by the cutting blades when the arms have deflected under centrifugal force, so that the tape will be cut by a blade and the fuel supply to the combustion chamber interrupted at the predetermined speed.

4. A gas turbine engine including a turbine, combustion chamber means capable of supplying working gases to said turbine, a fuel supply pipe leading to said combus- 4- tion chamber means, a stop valve in said fuel supply pipe, a tape arranged normally to hold open said stop valve and centrifugally-operable trigger means comprising a disc rotatable with said turbine, a plurality of symmetricallyarranged radially-extending arms each attached at the radially-outer end thereof to the periphery of the disc and each having an axially-extending limb at the radiallyinner end thereof, the arms being so pre-stressed that they are biased towards the adjacent face of the disc in opposition to centrifugal force tending to deflect the arms externally away from the face of the disc, the biasing being sufficient only to resist centrifugal force until a predetermined speed has been reached, a cutting blade carried on each axially-extending limb and so arranged that when the arms are deflected at said predetermined speed, the tape will be cut by a cutting blade and the stop valve 7 allowed to close.

References Cited in the file of this patent UNITED STATES PATENTS 

